1. Technical Field of the Invention
The present invention relates to a network session system that performs session such as joint performance of a plurality of electronic music terminals connected through a communication network such as the Internet.
2. Description of the Related Art
A technology for enabling musical session such as joint performance (ensemble) of musical instruments or chorus such as duet through the Internet is known in the art. For example, in an ensemble system described in Japanese Patent Publication No. 4259329, performance information representing a performance operation of a terminal (A) of a user is transmitted to another terminal (B) and is provided to a musical sound generation unit in the terminal (A) of the user after being delayed by a predetermined time, thereby allowing a musical sound generated according to the performance operation of the terminal (A) to be simultaneously emitted at the two terminals (A, B).
When session such as musical instrument ensemble or duet is conventionally performed through the Internet in an environment in which there is a certain amount of communication delay (for example, 30 ms) between two user terminals A and B as shown in FIG. 1(1), the user terminal A performs sound emission of performance such as musical instrument performance or singing of the user A with a delay of 30 ms to achieve synchronization with sound emission of performance such as musical instrument performance or singing of the user terminal B, and the user terminal B also performs sound emission of performance such as musical instrument performance or singing of the user B with a delay of 30 ms to achieve synchronization with sound emission of performance such as musical instrument performance or singing of the user terminal A. That is, in the conventional network session technology, one terminal performs session by transmitting performance data representing performance such as musical instrument performance or singing played on the terminal to another terminal and by receiving performance data representing performance such as musical instrument performance or singing played on said another terminal, and then simultaneously performing sound emission of the performance data of the terminal and sound emission of the performance data of said another terminal (and said another terminal also performs session in the same manner).
Here, the terminal delays the sound emission timing of performance of the terminal by a time corresponding to a communication delay so as to synchronize the performance sound of the terminal with the performance sound received from said another terminal. However, since the terminal user hears musical instrument performance or singing of the terminal user with a delay, the terminal user feels strangeness (or discomfort) and thus performers or singers cannot pleasantly play performance or singing.
For example, as shown in FIG. 1(2), an uneven delay occurs in some application case where users desire to sing a duet or to play a musical instrument ensemble along to back performance such as karaoke that is played on a terminal. For example, in the case where a user A of a user terminal A plays back performance and both the users A and B sing a duet on the user terminals A and B, the user B hears the back performance with a delay of 30 ms and hears the singing (or vocal) of the user A simultaneously with the back performance. However, the user A hears the singing of the user B with a round-trip delay of 60 ms from the back performance while hearing the back performance with a delay of 0 ms (i.e., without delay) as shown in FIG. 1(2)(a). This can be represented in a chronological manner as shown in FIG. 1(2)(b).
Session and duet could be performed without serious problems even in an environment where a considerable delay exists over the Internet in case that only one-way delay is caused at both parties as shown in FIG. 1(1). However, if there is a round-trip delay as shown in FIG. 1(2), the users hear transmitted performance unnaturally such that they feel strangeness, making it difficult to play joint performance.